A zinc pot roller for an al-zn plating production line and a preparation method thereof

Abstract

The application discloses a zinc pot roller for an aluminized zinc production line, which comprises a roller base body and a coating layer, wherein the roller base body is made of 317L stainless steel, and the chemical composition of the coating layer comprises the following components in percentage by mass: C: 0.1-0.15, Si: 2.0-3.0, B: 1.5-2.0, Cr: 25-27, Mo: 4-6, Co: 8-10, Nb: 0.5-0.8, Y2O3: 0.3-0.5, and the balance is Fe and inevitable impurities. The zinc pot roller has high corrosion resistance to molten aluminum-zinc liquid, high anti-zinc slag adhesion and high wear resistance, thereby prolonging the service life and ensuring the surface quality of the strip steel. Meanwhile, the application further discloses a preparation method of the zinc pot roller, which comprises the following steps: preparing the roller base body, preheating, laser cladding, intermediate heat treatment, machining, surface strengthening and detection, so that the metallurgical combination between the coating layer and the base body is ensured, and the thermal spraying coating layer is prevented from peeling off at high temperature.

Description

Technical Field

[0001] This invention relates to a zinc pot roller for use in an aluminum-zinc plating production line and its preparation method. Background Technology

[0002] Hot-dip galvanizing is divided into zinc plating and aluminized zinc plating. The zinc plating temperature is around 460℃, while the aluminized zinc plating temperature is around 600℃, meaning the aluminized zinc plating temperature is higher.

[0003] Currently, the coatings available on the market for zinc pot rollers are mainly for galvanized (460℃) coatings, and most of these coatings are prepared using thermal spraying processes, with the sprayed materials being primarily WC-type.

[0004] Because the working conditions on aluminized zinc plating production lines are more severe, the zinc pot rollers (including submerged rollers and stabilizing rollers) are immersed in molten aluminum and zinc at approximately 600°C for extended periods. The aluminum in the molten metal is highly corrosive to the iron substrate, easily forming brittle Fe-Al intermetallic compounds. Simultaneously, the zinc dross in the molten metal causes severe abrasive wear on the roller surface. Currently, the market practice is to use stainless steel rollers without coating. However, stainless steel rollers have poor wear and corrosion resistance, and in the later stages of production line use, a large amount of zinc dross adheres to them, causing surface quality defects in the strip steel. Therefore, they need to be replaced every 10-15 days, resulting in a short service life.

[0005] Some companies have proposed using spraying to prepare aluminum-zinc coated rollers, but this method has problems such as low bonding strength, high coating preparation cost, and pores in the coating that cause molten liquid to penetrate and peel off. Summary of the Invention

[0006] The problem this invention aims to solve is to provide a zinc pot roller for an aluminized zinc production line, which has high resistance to corrosion from molten aluminum and zinc, resistance to zinc dross adhesion, and wear resistance, thus extending its service life and ensuring the surface quality of the strip steel. Simultaneously, this invention also provides a method for preparing the zinc pot roller, which ensures the metallurgical bond between the coating and the substrate, avoiding the problem of thermal spray coating peeling off at high temperatures.

[0007] An invention relates to a zinc pot roller for an aluminum-zinc plating production line. The roller includes a roller substrate and a coating. The roller substrate is made of 317L stainless steel. The chemical composition and mass percentage of the coating are as follows: C: 0.1-0.15, Si: 2.0-3.0, B: 1.5-2.0, Cr: 25-27, Mo: 4-6, Co: 8-10, Nb: 0.5-0.8, Y2O3: 0.3-0.5, with the balance being Fe and unavoidable impurities.

[0008] The preferred chemical composition and mass percentage of the coating are: C: 0.1, Si: 2.0, B: 1.5, Cr: 25, Mo: 4, Co: 8, Nb: 0.5, Y2O3: 0.3, with the balance being Fe.

[0009] The preferred chemical composition and mass percentage of the coating are: C: 0.12, Si: 2.5, B: 1.75, Cr: 26, Mo: 5, Co: 9, Nb: 0.65, Y2O3: 0.4, with the balance being Fe.

[0010] The preferred chemical composition and mass percentage of the coating are: C: 0.15, Si: 3.0, B: 2.0, Cr: 27, Mo: 6, Co: 10, Nb: 0.8, Y2O3: 0.5, with the balance being Fe.

[0011] The method for preparing zinc pot rollers for aluminized zinc production lines of the present invention comprises the following steps: ① Roller substrate fabrication: The roller substrate is fabricated using centrifugal casting and machined to the required dimensions; ② Preheating: Preheat the zinc pot rollers to 120-150℃; ③ Laser cladding: Using synchronous powder feeding or pre-placed powder, a fiber laser is used for cladding; the process parameters are: laser power 5500-6000W, scanning speed 500-600mm / min, spot size 20*2mm, overlap rate 40%, the cladding process is carried out in two layers, the first layer cladding thickness is 1.3-1.5mm, and the second layer cladding thickness is 1.3-1.5mm. ④ Intermediate heat treatment: After each layer of cladding is completed, stress-relief annealing heat treatment is performed at a temperature of 520-550℃, held for 5-8 hours, and then cooled in the furnace; a total of two heat treatments are performed. ⑤ Machining: Perform roller turning according to the dimensions in the drawing, retaining an effective thickness of not less than 2mm for the cladding layer; ⑥ Surface strengthening: The roller surface is strengthened by ultrasonic rolling; ⑦ Testing: Conduct penetration testing and hardness testing on the cladding layer.

[0012] Step ①: After the roller substrate is manufactured, the surface of the roller substrate needs to be degreased and derusted by cleaning with anhydrous ethanol or acetone until there are no stains.

[0013] Step ②: Before preheating, accurately weigh the alloy powder according to the mass percentage, mix the powder evenly, and dry it in a vacuum.

[0014] The heat treatment in step ④ is carried out in a normal atmosphere.

[0015] In step ⑥, surface strengthening, the parameters for ultrasonic rolling are: static pressure 400N and amplitude 10μm.

[0016] The advantages of the coating material for the zinc pot roller used in the aluminized zinc production line of this invention are: 1. Cr: High Cr content (25-27%) preferentially forms a dense Cr2O3 oxide film on the coating surface at high temperatures, effectively blocking the inward diffusion of Al atoms; it dissolves in the matrix to increase the electrode potential and enhance electrochemical corrosion resistance; 2. Ni: It works synergistically with Fe to reduce the interdiffusion of Fe and Al, inhibiting the formation of brittle Fe-Al intermetallic compounds (such as Fe2Al5); it works with Cr to maintain the austenitic phase and avoid high-temperature phase transformation cracking; 3. Mo: An appropriate amount of Mo (4-6%) improves the coating... The coating exhibits excellent resistance to pitting and reducing media corrosion, particularly showing significant inhibition against the erosion of liquid Al and Zn; solid solution strengthening enhances high-temperature strength and reduces high-temperature creep; 4. Nb: forms NbC with carbides to pin grain boundaries, refining the cladding layer structure; dispersed Nb particles prevent aluminum atoms from diffusing along grain boundaries; 5. Co: the addition of Co (8-10%) strengthens the iron matrix through solid solution, improving the high-temperature strength of the coating at around 600℃; 6. Rare earth oxide Y2O3: refines grains, improves the adhesion between the oxide film and the substrate, preventing peeling; purifies grain boundaries, reducing impurity segregation. Therefore, the zinc pot roller of this invention possesses excellent resistance to molten aluminum and zinc corrosion, resistance to zinc slag adhesion, and wear resistance, while also being metallurgically integrated with the substrate, avoiding the problem of thermal spray coating peeling off at high temperatures.

[0017] The advantages of the preparation method of the zinc pot roller for the aluminized zinc production line of the present invention are: 1. The bonding strength between the coating and the substrate is extremely high: the coating layer is obtained by laser cladding on the surface of the roller substrate, and the coating and the substrate are metallurgically bonded, with a bonding strength far higher than that of thermal spraying; 2. The use of two-layer cladding avoids the problems of large heat input and large internal stress of single-layer cladding. At the same time, a heat treatment is performed after each layer of cladding, which can effectively release the huge internal stress generated during the laser cladding process, and avoid the deformation and cracking of the roller in the zinc pot (600℃) due to the presence of internal stress, while ensuring product quality: the improvement of surface integrity ensures product quality; 3. The final ultrasonic rolling treatment not only reduces slag points, but also refines the surface grains to the nanoscale through plastic deformation, forming a hardened layer, further extending the service life of the roller.

[0018] Therefore, the zinc pot roller of this invention, through the combination of coating selection and preparation methods, exhibits excellent resistance to corrosion from molten aluminum-zinc liquid, resistance to zinc slag adhesion, and wear resistance at around 600℃. Furthermore, the high bonding strength between the cladding layer and the substrate prevents peeling. Simultaneously, since the cladding layer thickness is not less than 2mm, after each cycle, the surface coating (≤0.5mm) can be removed by grinding, allowing for reuse more than three times with a single cladding, significantly reducing costs. Therefore, the lifespan of the zinc pot roller of this invention is more than twice that of existing zinc pot rollers. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments.

[0020] Example 1 This invention relates to a zinc pot roller for an aluminized zinc plating production line. The base material of the zinc pot roller is selected from 317L stainless steel, with a diameter of φ50mm and a length of 200mm. The specific steps of its preparation method are as follows: ① Making the roller base: The roller base is made using centrifugal casting and machined to the required dimensions; the surface of the roller base is degreased and derusted, and cleaned with anhydrous ethanol or acetone until there are no stains. ②Ingredients: Accurately weigh the alloy powder according to the following mass percentages: C 0.12%, Si 2.5%, B 1.75%, Cr 26%, Mo 5%, Co 9%, Nb 0.65%, Y2O3 0.4%, Fe balance. Mix the powder evenly and dry it in a vacuum. ③ Preheating: Preheat the entire or surface of the cleaned roller substrate to 135°C to remove surface-adsorbed moisture and reduce the temperature gradient during the cladding process; ④ First cladding: Laser cladding equipment was used with the following parameters set: power 5800W, scanning speed 550mm / min, spot size 20×2mm, overlap rate 40%, and argon protection; the first cladding layer thickness was 1.4mm. ⑤ First heat treatment: Place the roller in a heat treatment furnace, hold at 530℃ for 6 hours, and then cool to room temperature with the furnace; ⑥ Second cladding: A second cladding layer is applied on top of the first layer, with the same parameters as above and a thickness of 1.4 mm; ⑦ Second heat treatment: Hold at 530℃ for 6 hours again; ⑧ Machining: Turn on a lathe to the dimensions shown in the drawing, retaining a cladding layer thickness of 2.0mm; ⑨ Ultrasonic rolling: The roller surface is treated using ultrasonic rolling equipment with the following parameters: static pressure 400N, amplitude 10μm; the surface grains are refined by high-frequency impact, the surface hardness is increased and compressive stress is introduced, and the smoothness of the roller surface is improved at the same time.

[0021] ⑩ Inspection: Penetrant testing showed no defects; surface hardness test result was HRC 58-62, with good uniformity.

[0022] Meanwhile, two 317L stainless steel round bars with a diameter of φ50 and a length of 200mm were taken. One bar was left untreated, while the other bar was coated with MoB CoCr to form Comparative Example 1 and Comparative Example 2. The three round bars of Example 1, Comparative Example 1, and Comparative Example 2 were placed in molten aluminum-zinc solution (600℃) and rotated continuously. The surface coating status was observed every 5 days, and its performance is shown in the table below.

[0023]

[0024] The zinc pot roller of this invention was applied to the aluminized zinc production line of a steel plant. After 30 days of continuous operation, it was inspected after being taken off the line. The roller surface was smooth, with no obvious corrosion pits or zinc slag adhesion. Its service life was more than twice that of traditional thermal spraying rollers.

Claims

1. A zinc pot roller for an aluminized zinc production line, comprising a roller substrate, characterized in that: It also includes a coating. The roller substrate is 317L stainless steel. The chemical composition and mass percentage of the coating are: C: 0.1-0.15, Si: 2.0-3.0, B: 1.5-2.0, Cr: 25-27, Mo: 4-6, Co: 8-10, Nb: 0.5-0.8, Y2O3: 0.3-0.5, with the balance being Fe and unavoidable impurities.

2. The zinc pot roller for an aluminized zinc production line according to claim 1, characterized in that: The preferred chemical composition and mass percentage of the coating are: C: 0.1, Si: 2.0, B: 1.5, Cr: 25, Mo: 4, Co: 8, Nb: 0.5, Y2O3: 0.3, with the balance being Fe.

3. The zinc pot roller for an aluminized zinc production line according to claim 1, characterized in that: The preferred chemical composition and mass percentage of the coating are: C: 0.12, Si: 2.5, B: 1.75, Cr: 26, Mo: 5, Co: 9, Nb: 0.65, Y2O3: 0.4, with the balance being Fe.

4. The zinc pot roller for an aluminized zinc production line according to claim 1, characterized in that: The preferred chemical composition and mass percentage of the coating are: C: 0.15, Si: 3.0, B: 2.0, Cr: 27, Mo: 6, Co: 10, Nb: 0.8, Y2O3: 0.5, with the balance being Fe.

5. The method for preparing the zinc pot roller for the aluminized zinc production line according to any one of claims 1-4, comprising the following steps: ① Roller substrate fabrication: The roller substrate is fabricated using centrifugal casting and machined to the required dimensions; ② Preheating: Preheat the roller substrate to 120-150℃; ③ Laser cladding: Using synchronous powder feeding or pre-placed powder, a fiber laser is used for cladding; the process parameters are: laser power 5500-6000W, scanning speed 500-600mm / min, spot size 20*2mm, overlap rate 40%, the cladding process is carried out in two layers, the first layer cladding thickness is 1.3-1.5mm, and the second layer cladding thickness is 1.3-1.5mm. ④ Intermediate heat treatment: After each layer of cladding is completed, stress-relief annealing heat treatment is performed at a temperature of 520-550℃, held for 5-8 hours, and then cooled in the furnace; a total of two heat treatments are performed. ⑤ Machining: Perform roller turning according to the dimensions in the drawing, retaining an effective thickness of not less than 2mm for the cladding layer; ⑥ Surface strengthening: The roller surface is strengthened by ultrasonic rolling; ⑦ Testing: Conduct penetration testing and hardness testing on the cladding layer.

6. The method for preparing zinc pot rollers for aluminized zinc production lines according to claim 5 is characterized in that: Step ①: After the roller substrate is made, the surface of the roller substrate needs to be degreased and derusted by cleaning with anhydrous ethanol or acetone until there are no stains.

7. The method for preparing zinc pot rollers for aluminized zinc production lines according to claim 5, characterized in that: Before preheating in step ②, accurately weigh the alloy powder according to the mass percentage, mix the powder evenly, and dry it in a vacuum.

8. The method for preparing zinc pot rollers for aluminized zinc production lines according to claim 5, characterized in that: The heat treatment in step ④ is carried out in a normal atmosphere.

9. The method for preparing zinc pot rollers for aluminized zinc production lines according to claim 5, characterized in that: Step 6 Surface strengthening: The parameters for ultrasonic rolling are: static pressure 400N, amplitude 10μm.

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